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Recording-2025-02-13T17_46_16.965Z

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Recording-2025-02-13T17_46_16.965Z

Introduction to the Motor System

  • The motor system is responsible for impulses originating from the central nervous system and reaching the body.

  • Two subdivisions:

    • Somatic Nervous System: Innervates skeletal muscles.

    • Autonomic Nervous System: Innervates smooth and cardiac muscles, typically under involuntary control.

Somatic Nervous System

  • Regulators of skeletal muscle function.

  • Important for voluntary movements and related to the next topic of skeletal muscles.

Anatomy Overview

  • Impulses originate from the brain, influencing muscle movement.

  • Cerebellum: Integrates sensory information related to equilibrium, balance, and proprioception.

  • Sensory Receptors:

    • Muscle Spindles: Located within skeletal muscles, providing feedback on muscle length and rate of change.

    • Golgi Tendon Organs: Embedded in tendons, providing information on muscle tension.

Organization of Somatic Motor System

  • Lower Motor Neurons:

    • Located in the ventral horn of the spinal cord or brainstem.

    • Travel to skeletal muscles through the ventral root of spinal nerves.

    • Function as a final common pathway (one neuron to one muscle).

    • Influenced by sensory feedback, which may have facilitatory or inhibitory effects.

Motor Pathway Circuits

  1. Lower Motor Neurons:

    • Located in the brainstem/spinal cord.

    • Directly responsible for muscle contraction.

    • Evidence of commissural and ipsilateral tracts.

  2. Upper Motor Neurons:

    • Input to lower motor neurons, playing key roles in voluntary movements.

    • Examples include direct and indirect motor pathways from the brain.

  3. Basal Ganglia System:

    • Regulates initiation and control of motor responses based on sensory input and feedback.

    • Plays a significant role in forming correct motor responses.

    • Degeneration Example: Huntington's disease demonstrates how basal nuclei degeneration affects movement control.

Role of Cerebellum

  • Acts like a ‘tattle tale’ to the primary motor cortex by comparing intended movements with actual movements.

  • Functions under high complexity due to continuous sensory input and motor command integration.

Direct and Indirect Motor Pathways

  • Direct Motor Pathways:

    • Deliver signals from the cerebral cortex to lower motor neurons, controlling voluntary movements.

  • Indirect Motor Pathways:

    • Involved in reflexes and posture control.

    • Corticospinal Pathways: Includes lateral and anterior corticospinal tracts.

  • Hyperdirect Pathway: Rapidly influences motor control independently of voluntary processes.

Basal Ganglia and Voluntary Movement

  • Comprised of structures like the caudate nucleus, putamen, and globus pallidus, crucial for motor control.

  • Involvement in voluntary movement selection and abnormal movement patterns in disorders like Huntington's disease.

Cerebellum's Motor Functions

  • Coordinates voluntary muscle movements by processing incoming sensory information from various sources (muscles, joints, ears, eyes).

  • Sends corrective signals to the motor cortex rather than directly influencing muscle contractions.

Cerebellar Input and Output

  • Cerebellar pathways receive input from different sources to ensure precise motor output.

  • Highlights the distinction between actual movements and intended movements via corrections sent to the primary motor cortex.

Conclusion

  • The motor system encompasses a complex interaction between the central nervous system and muscles, with specific pathways and structures playing pivotal roles in coordinating voluntary and involuntary muscle movements.